Liquid crystal does not illuminate any light by itself. Therefore, an external light source is required in a liquid crystal display (LCD). Typically, a backlight module is used in a transmission thin film transistor (TFT) liquid crystal display (LCD) for providing required light. Cold cathode fluorescent lamps (CCFLs) or light emitting diodes (LEDs) are the light source in a backlight module. A high brightness efficiency and a long lifetime make the cold cathode fluorescent lamps (CCFLs) popular for use in backlight modules.
Light modules can be divided into two types, back and front. The back type can be further divided into two types, edge-lit and direct-lit. The edge-lit backlight module can provide an average brightness with an efficiency of about 50%. Moreover, the edge-lit backlight module is thin and lightweight. Therefore, it can be used in a portable color LCD. In comparison, the brightness efficiency of the bottom-lit backlight module is about 60%. However, it is heavier and thicker. Therefore, the bottom-lit backlight module is always used in LCD monitors and LCD televisions.
Furthermore, when the LCD monitor is larger than 17 inches, the weight of the bottom-lit backlight module is actually less than the weight of the edge-lit backlight module. Therefore, there is no advantage to using the edge-lit backlight module for large-scale LCD televisions, and the trend is to use the bottom-lit backlight module instead.
Referring to FIG. 1A, a schematic top view of a conventional bottom-lit backlight module is illustrated. Several CCFLs 100 are arranged in parallel to each other so as to provide light to a LCD panel (not shown in this figure). FIG. 1B illustrates a schematic sectional view along the AA′ line of FIG. 1A. The light emitted from the CCFLs 100 is reflected by the reflective plate 102. The reflected light is diffused by the scattering plate 104 to provide a uniform backlight to the LCD panel. However, the image displayed on the LCD panel is often degraded by what appear to be various illumination and shadows, which are caused by the presence of the CCFLs arranged underneath the panel. A backlight module that does not cause the various illumination and shadows on the display is thus required.